FreeBSD/Linux Kernel Cross Reference
sys/net/ppp_tty.c

     /*
      * ppp_tty.c - Point-to-Point Protocol (PPP) driver for asynchronous
      *             tty devices.
      *
      * Copyright (c) 1989 Carnegie Mellon University.
      * All rights reserved.
      *
      * Redistribution and use in source and binary forms are permitted
      * provided that the above copyright notice and this paragraph are
     * duplicated in all such forms and that any documentation,
     * advertising materials, and other materials related to such
     * distribution and use acknowledge that the software was developed
     * by Carnegie Mellon University.  The name of the
     * University may not be used to endorse or promote products derived
     * from this software without specific prior written permission.
     * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
     * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
     * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
     *
     * Drew D. Perkins
     * Carnegie Mellon University
     * 4910 Forbes Ave.
     * Pittsburgh, PA 15213
     * (412) 268-8576
     * ddp@andrew.cmu.edu
     *
     * Based on:
     *      @(#)if_sl.c     7.6.1.2 (Berkeley) 2/15/89
     *
     * Copyright (c) 1987 Regents of the University of California.
     * All rights reserved.
     *
     * Redistribution and use in source and binary forms are permitted
     * provided that the above copyright notice and this paragraph are
     * duplicated in all such forms and that any documentation,
     * advertising materials, and other materials related to such
     * distribution and use acknowledge that the software was developed
     * by the University of California, Berkeley.  The name of the
     * University may not be used to endorse or promote products derived
     * from this software without specific prior written permission.
     * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
     * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
     * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
     *
     * Serial Line interface
     *
     * Rick Adams
     * Center for Seismic Studies
     * 1300 N 17th Street, Suite 1450
     * Arlington, Virginia 22209
     * (703)276-7900
     * rick@seismo.ARPA
     * seismo!rick
     *
     * Pounded on heavily by Chris Torek (chris@mimsy.umd.edu, umcp-cs!chris).
     * Converted to 4.3BSD Beta by Chris Torek.
     * Other changes made at Berkeley, based in part on code by Kirk Smith.
     *
     * Converted to 4.3BSD+ 386BSD by Brad Parker (brad@cayman.com)
     * Added VJ tcp header compression; more unified ioctls
     *
     * Extensively modified by Paul Mackerras (paulus@cs.anu.edu.au).
     * Cleaned up a lot of the mbuf-related code to fix bugs that
     * caused system crashes and packet corruption.  Changed pppstart
     * so that it doesn't just give up with a "collision" if the whole
     * packet doesn't fit in the output ring buffer.
     *
     * Added priority queueing for interactive IP packets, following
     * the model of if_sl.c, plus hooks for bpf.
     * Paul Mackerras (paulus@cs.anu.edu.au).
     */
    
    /* $FreeBSD: releng/5.3/sys/net/ppp_tty.c 136588 2004-10-16 08:43:07Z cvs2svn $ */
    
    #include "opt_ppp.h"            /* XXX for ppp_defs.h */
    
    #define VJC                     /* XXX for ppp_defs.h */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/proc.h>
    #include <sys/mbuf.h>
    #include <sys/socket.h>
    #include <sys/fcntl.h>
    #include <sys/tty.h>
    #include <sys/conf.h>
    #include <sys/uio.h>
    #include <sys/vnode.h>
    
    #ifdef PPP_FILTER
    #include <net/bpf.h>
    #endif
    #include <net/if_ppp.h>
    #include <net/if_pppvar.h>
    
    static int      pppopen(struct cdev *dev, struct tty *tp);
    static int      pppclose(struct tty *tp, int flag);
    static int      pppread(struct tty *tp, struct uio *uio, int flag);
    static int      pppwrite(struct tty *tp, struct uio *uio, int flag);
   static int      ppptioctl(struct tty *tp, u_long cmd, caddr_t data,
                                           int flag, struct thread *td);
   static int      pppinput(int c, struct tty *tp);
   static int      pppstart(struct tty *tp);
   
   static u_short  pppfcs(u_short fcs, u_char *cp, int len);
   static void     pppasyncstart(struct ppp_softc *);
   static void     pppasyncctlp(struct ppp_softc *);
   static void     pppasyncrelinq(struct ppp_softc *);
   static void     pppasyncsetmtu(struct ppp_softc *);
   static void     ppp_timeout(void *);
   static void     pppgetm(struct ppp_softc *sc);
   static void     ppplogchar(struct ppp_softc *, int);
   
   /* XXX called from if_ppp.c - layering violation */
   void            pppasyncattach(void *);
   void            pppasyncdetach(void);
   
   /*
    * Some useful mbuf macros not in mbuf.h.
    */
   #define M_IS_CLUSTER(m) ((m)->m_flags & M_EXT)
   
   #define M_DATASTART(m)  \
           (M_IS_CLUSTER(m) ? (m)->m_ext.ext_buf : \
               (m)->m_flags & M_PKTHDR ? (m)->m_pktdat : (m)->m_dat)
   
   #define M_DATASIZE(m)   \
           (M_IS_CLUSTER(m) ? (m)->m_ext.ext_size : \
               (m)->m_flags & M_PKTHDR ? MHLEN: MLEN)
   
   /*
    * Does c need to be escaped?
    */
   #define ESCAPE_P(c)     (sc->sc_asyncmap[(c) >> 5] & (1 << ((c) & 0x1F)))
   
   /*
    * Procedures for using an async tty interface for PPP.
    */
   
   /* This is a FreeBSD-2.X kernel. */
   #define CCOUNT(q)       ((q)->c_cc)
   #define PPP_LOWAT       100     /* Process more output when < LOWAT on queue */
   #define PPP_HIWAT       400     /* Don't start a new packet if HIWAT on que */
   
   /*
    * Define the PPP line discipline.
    */
   
   static struct linesw pppdisc = {
           pppopen,        pppclose,       pppread,        pppwrite,
           ppptioctl,      pppinput,       pppstart,       ttymodem
   };
   
   void
   pppasyncattach(dummy)
       void *dummy;
   {
       ldisc_register(PPPDISC, &pppdisc);
   }
   
   void
   pppasyncdetach()
   {
       ldisc_deregister(PPPDISC);
   }
   
   /*
    * Line specific open routine for async tty devices.
    * Attach the given tty to the first available ppp unit.
    * Called from device open routine or ttioctl() at >= splsofttty()
    */
   /* ARGSUSED */
   static int
   pppopen(dev, tp)
       struct cdev *dev;
       register struct tty *tp;
   {
       struct thread *td = curthread;              /* XXX */
       register struct ppp_softc *sc;
       int error, s;
   
       if ((error = suser(td)) != 0)
           return (error);
   
       s = spltty();
   
       tp->t_hotchar = PPP_FLAG;
   
       if ((sc = pppalloc(td->td_proc->p_pid)) == NULL) {
           splx(s);
           return ENXIO;
       }
   
       if (sc->sc_relinq)
           (*sc->sc_relinq)(sc);   /* get previous owner to relinquish the unit */
   
       sc->sc_ilen = 0;
       sc->sc_m = NULL;
       bzero(sc->sc_asyncmap, sizeof(sc->sc_asyncmap));
       sc->sc_asyncmap[0] = 0xffffffff;
       sc->sc_asyncmap[3] = 0x60000000;
       sc->sc_rasyncmap = 0;
       sc->sc_devp = (void *) tp;
       sc->sc_start = pppasyncstart;
       sc->sc_ctlp = pppasyncctlp;
       sc->sc_relinq = pppasyncrelinq;
       sc->sc_setmtu = pppasyncsetmtu;
       sc->sc_outm = NULL;
       pppgetm(sc);
       sc->sc_if.if_flags |= IFF_RUNNING;
       getmicrotime(&sc->sc_if.if_lastchange);
       sc->sc_if.if_baudrate = tp->t_ospeed;
   
       tp->t_sc = (caddr_t) sc;
       tp->t_hotchar = PPP_FLAG;
       ttyflush(tp, FREAD | FWRITE);
   
       /*
        * Pre-allocate cblocks to the "just right" amount.  The 1 byte t_canq
        * allocation helps avoid the need for select and/or FIONREAD.
        * We also pass 1 byte tokens through t_canq...
        */
       clist_alloc_cblocks(&tp->t_canq, 1, 1);
       clist_alloc_cblocks(&tp->t_outq, sc->sc_if.if_mtu + PPP_HIWAT,
                           sc->sc_if.if_mtu + PPP_HIWAT);
       clist_alloc_cblocks(&tp->t_rawq, 0, 0);
   
       splx(s);
   
       return (0);
   }
   
   /*
    * Line specific close routine, called from device close routine
    * and from ttioctl at >= splsofttty().
    * Detach the tty from the ppp unit.
    * Mimics part of tty_close().
    */
   static int
   pppclose(tp, flag)
       struct tty *tp;
       int flag;
   {
       register struct ppp_softc *sc;
       int s;
   
       s = spltty();
       ttyflush(tp, FREAD | FWRITE);
       clist_free_cblocks(&tp->t_canq);
       clist_free_cblocks(&tp->t_outq);
       sc = (struct ppp_softc *) tp->t_sc;
       if (sc != NULL) {
           tp->t_sc = NULL;
           if (tp == (struct tty *) sc->sc_devp) {
               pppasyncrelinq(sc);
               pppdealloc(sc);
           }
       }
       splx(s);
       return 0;
   }
   
   /*
    * Relinquish the interface unit to another device.
    */
   static void
   pppasyncrelinq(sc)
       struct ppp_softc *sc;
   {
       int s;
   
       s = spltty();
       if (sc->sc_outm) {
           m_freem(sc->sc_outm);
           sc->sc_outm = NULL;
       }
       if (sc->sc_m) {
           m_freem(sc->sc_m);
           sc->sc_m = NULL;
       }
       if (sc->sc_flags & SC_TIMEOUT) {
           untimeout(ppp_timeout, (void *) sc, sc->sc_ch);
           sc->sc_flags &= ~SC_TIMEOUT;
       }
       splx(s);
   }
   
   /*
    * This gets called from the upper layer to notify a mtu change
    */
   static void
   pppasyncsetmtu(sc)
   register struct ppp_softc *sc;
   {
       register struct tty *tp = (struct tty *) sc->sc_devp;
       int s;
   
       s = spltty();
       if (tp != NULL)
           clist_alloc_cblocks(&tp->t_outq, sc->sc_if.if_mtu + PPP_HIWAT,
                                sc->sc_if.if_mtu + PPP_HIWAT);
       splx(s);
   }
   
   /*
    * Line specific (tty) read routine.
    * called at zero spl from the device driver in the response to user-level
    * reads on the tty file descriptor (ie: pppd).
    */
   static int
   pppread(tp, uio, flag)
       register struct tty *tp;
       struct uio *uio;
       int flag;
   {
       register struct ppp_softc *sc = (struct ppp_softc *)tp->t_sc;
       struct mbuf *m, *m0;
       register int s;
       int error = 0;
   
       if (sc == NULL)
           return 0;
       /*
        * Loop waiting for input, checking that nothing disasterous
        * happens in the meantime.
        */
       s = spltty();
       for (;;) {
           if (tp != (struct tty *) sc->sc_devp || tp->t_line != PPPDISC) {
               splx(s);
               return 0;
           }
           if (sc->sc_inq.ifq_head != NULL)
               break;
           if ((tp->t_state & TS_CONNECTED) == 0) {
               splx(s);
               return 0;           /* end of file */
           }
           if (tp->t_state & TS_ASYNC || flag & IO_NDELAY) {
               splx(s);
               return (EWOULDBLOCK);
           }
           error = ttysleep(tp, TSA_HUP_OR_INPUT(tp), TTIPRI | PCATCH, "pppin", 0);
           if (error) {
               splx(s);
               return error;
           }
       }
   
       /* Pull place-holder byte out of canonical queue */
       getc(&tp->t_canq);
   
       /* Get the packet from the input queue */
       IF_DEQUEUE(&sc->sc_inq, m0);
       splx(s);
   
       for (m = m0; m && uio->uio_resid; m = m->m_next)
           if ((error = uiomove(mtod(m, u_char *), m->m_len, uio)) != 0)
               break;
       m_freem(m0);
       return (error);
   }
   
   /*
    * Line specific (tty) write routine.
    * called at zero spl from the device driver in the response to user-level
    * writes on the tty file descriptor (ie: pppd).
    */
   static int
   pppwrite(tp, uio, flag)
       register struct tty *tp;
       struct uio *uio;
       int flag;
   {
       register struct ppp_softc *sc = (struct ppp_softc *)tp->t_sc;
       struct mbuf *m, *m0, **mp;
       struct sockaddr dst;
       int len, error, s;
   
       if ((tp->t_state & TS_CONNECTED) == 0)
           return 0;               /* wrote 0 bytes */
       if (tp->t_line != PPPDISC)
           return (EINVAL);
       if (sc == NULL || tp != (struct tty *) sc->sc_devp)
           return EIO;
       if (uio->uio_resid > sc->sc_if.if_mtu + PPP_HDRLEN ||
           uio->uio_resid < PPP_HDRLEN)
           return (EMSGSIZE);
   
       s = spltty();
       for (mp = &m0; uio->uio_resid; mp = &m->m_next) {
           MGET(m, M_TRYWAIT, MT_DATA);
           if ((*mp = m) == NULL) {
               m_freem(m0);
               splx(s);
               return (ENOBUFS);
           }
           m->m_len = 0;
           if (uio->uio_resid >= MCLBYTES / 2)
               MCLGET(m, M_DONTWAIT);
           len = M_TRAILINGSPACE(m);
           if (len > uio->uio_resid)
               len = uio->uio_resid;
           if ((error = uiomove(mtod(m, u_char *), len, uio)) != 0) {
               m_freem(m0);
               splx(s);
               return (error);
           }
           m->m_len = len;
       }
       dst.sa_family = AF_UNSPEC;
       bcopy(mtod(m0, u_char *), dst.sa_data, PPP_HDRLEN);
       m0->m_data += PPP_HDRLEN;
       m0->m_len -= PPP_HDRLEN;
   
       /* call the upper layer to "transmit" it... */
       error = pppoutput(&sc->sc_if, m0, &dst, (struct rtentry *)0);
       splx(s);
       return (error);
   }
   
   /*
    * Line specific (tty) ioctl routine.
    * This discipline requires that tty device drivers call
    * the line specific l_ioctl routine from their ioctl routines.
    */
   /* ARGSUSED */
   static int
   ppptioctl(tp, cmd, data, flag, td)
       struct tty *tp;
       u_long cmd;
       caddr_t data;
       int flag;
       struct thread *td;
   {
       struct ppp_softc *sc = (struct ppp_softc *) tp->t_sc;
       int error, s;
   
       if (sc == NULL || tp != (struct tty *) sc->sc_devp)
           return (ENOIOCTL);
   
       error = 0;
       switch (cmd) {
       case PPPIOCSASYNCMAP:
           if ((error = suser(td)) != 0)
               break;
           sc->sc_asyncmap[0] = *(u_int *)data;
           break;
   
       case PPPIOCGASYNCMAP:
           *(u_int *)data = sc->sc_asyncmap[0];
           break;
   
       case PPPIOCSRASYNCMAP:
           if ((error = suser(td)) != 0)
               break;
           sc->sc_rasyncmap = *(u_int *)data;
           break;
   
       case PPPIOCGRASYNCMAP:
           *(u_int *)data = sc->sc_rasyncmap;
           break;
   
       case PPPIOCSXASYNCMAP:
           if ((error = suser(td)) != 0)
               break;
           s = spltty();
           bcopy(data, sc->sc_asyncmap, sizeof(sc->sc_asyncmap));
           sc->sc_asyncmap[1] = 0;             /* mustn't escape 0x20 - 0x3f */
           sc->sc_asyncmap[2] &= ~0x40000000;  /* mustn't escape 0x5e */
           sc->sc_asyncmap[3] |= 0x60000000;   /* must escape 0x7d, 0x7e */
           splx(s);
           break;
   
       case PPPIOCGXASYNCMAP:
           bcopy(sc->sc_asyncmap, data, sizeof(sc->sc_asyncmap));
           break;
   
       default:
           error = pppioctl(sc, cmd, data, flag, td);
           if (error == 0 && cmd == PPPIOCSMRU)
               pppgetm(sc);
       }
   
       return error;
   }
   
   /*
    * FCS lookup table as calculated by genfcstab.
    */
   static u_short fcstab[256] = {
           0x0000, 0x1189, 0x2312, 0x329b, 0x4624, 0x57ad, 0x6536, 0x74bf,
           0x8c48, 0x9dc1, 0xaf5a, 0xbed3, 0xca6c, 0xdbe5, 0xe97e, 0xf8f7,
           0x1081, 0x0108, 0x3393, 0x221a, 0x56a5, 0x472c, 0x75b7, 0x643e,
           0x9cc9, 0x8d40, 0xbfdb, 0xae52, 0xdaed, 0xcb64, 0xf9ff, 0xe876,
           0x2102, 0x308b, 0x0210, 0x1399, 0x6726, 0x76af, 0x4434, 0x55bd,
           0xad4a, 0xbcc3, 0x8e58, 0x9fd1, 0xeb6e, 0xfae7, 0xc87c, 0xd9f5,
           0x3183, 0x200a, 0x1291, 0x0318, 0x77a7, 0x662e, 0x54b5, 0x453c,
           0xbdcb, 0xac42, 0x9ed9, 0x8f50, 0xfbef, 0xea66, 0xd8fd, 0xc974,
           0x4204, 0x538d, 0x6116, 0x709f, 0x0420, 0x15a9, 0x2732, 0x36bb,
           0xce4c, 0xdfc5, 0xed5e, 0xfcd7, 0x8868, 0x99e1, 0xab7a, 0xbaf3,
           0x5285, 0x430c, 0x7197, 0x601e, 0x14a1, 0x0528, 0x37b3, 0x263a,
           0xdecd, 0xcf44, 0xfddf, 0xec56, 0x98e9, 0x8960, 0xbbfb, 0xaa72,
           0x6306, 0x728f, 0x4014, 0x519d, 0x2522, 0x34ab, 0x0630, 0x17b9,
           0xef4e, 0xfec7, 0xcc5c, 0xddd5, 0xa96a, 0xb8e3, 0x8a78, 0x9bf1,
           0x7387, 0x620e, 0x5095, 0x411c, 0x35a3, 0x242a, 0x16b1, 0x0738,
           0xffcf, 0xee46, 0xdcdd, 0xcd54, 0xb9eb, 0xa862, 0x9af9, 0x8b70,
           0x8408, 0x9581, 0xa71a, 0xb693, 0xc22c, 0xd3a5, 0xe13e, 0xf0b7,
           0x0840, 0x19c9, 0x2b52, 0x3adb, 0x4e64, 0x5fed, 0x6d76, 0x7cff,
           0x9489, 0x8500, 0xb79b, 0xa612, 0xd2ad, 0xc324, 0xf1bf, 0xe036,
           0x18c1, 0x0948, 0x3bd3, 0x2a5a, 0x5ee5, 0x4f6c, 0x7df7, 0x6c7e,
           0xa50a, 0xb483, 0x8618, 0x9791, 0xe32e, 0xf2a7, 0xc03c, 0xd1b5,
           0x2942, 0x38cb, 0x0a50, 0x1bd9, 0x6f66, 0x7eef, 0x4c74, 0x5dfd,
           0xb58b, 0xa402, 0x9699, 0x8710, 0xf3af, 0xe226, 0xd0bd, 0xc134,
           0x39c3, 0x284a, 0x1ad1, 0x0b58, 0x7fe7, 0x6e6e, 0x5cf5, 0x4d7c,
           0xc60c, 0xd785, 0xe51e, 0xf497, 0x8028, 0x91a1, 0xa33a, 0xb2b3,
           0x4a44, 0x5bcd, 0x6956, 0x78df, 0x0c60, 0x1de9, 0x2f72, 0x3efb,
           0xd68d, 0xc704, 0xf59f, 0xe416, 0x90a9, 0x8120, 0xb3bb, 0xa232,
           0x5ac5, 0x4b4c, 0x79d7, 0x685e, 0x1ce1, 0x0d68, 0x3ff3, 0x2e7a,
           0xe70e, 0xf687, 0xc41c, 0xd595, 0xa12a, 0xb0a3, 0x8238, 0x93b1,
           0x6b46, 0x7acf, 0x4854, 0x59dd, 0x2d62, 0x3ceb, 0x0e70, 0x1ff9,
           0xf78f, 0xe606, 0xd49d, 0xc514, 0xb1ab, 0xa022, 0x92b9, 0x8330,
           0x7bc7, 0x6a4e, 0x58d5, 0x495c, 0x3de3, 0x2c6a, 0x1ef1, 0x0f78
   };
   
   /*
    * Calculate a new FCS given the current FCS and the new data.
    */
   static u_short
   pppfcs(u_short fcs, u_char *cp, int len)
   {
       while (len--)
           fcs = PPP_FCS(fcs, *cp++);
       return (fcs);
   }
   
   /*
    * This gets called at splsoftnet from if_ppp.c at various times
    * when there is data ready to be sent.
    */
   static void
   pppasyncstart(sc)
       register struct ppp_softc *sc;
   {
       register struct tty *tp = (struct tty *) sc->sc_devp;
       register struct mbuf *m;
       register int len;
       register u_char *start, *stop, *cp;
       int n, ndone, done, idle;
       int s;
   
       idle = 0;
       /* XXX assumes atomic access to *tp although we're not at spltty(). */
       while (CCOUNT(&tp->t_outq) < PPP_HIWAT) {
           /*
            * See if we have an existing packet partly sent.
            * If not, get a new packet and start sending it.
            */
           m = sc->sc_outm;
           if (m == NULL) {
               /*
                * Get another packet to be sent.
                */
               m = ppp_dequeue(sc);
               if (m == NULL) {
                   idle = 1;
                   break;
               }
   
               /*
                * The extra PPP_FLAG will start up a new packet, and thus
                * will flush any accumulated garbage.  We do this whenever
                * the line may have been idle for some time.
                */
               /* XXX as above. */
               if (CCOUNT(&tp->t_outq) == 0) {
                   ++sc->sc_stats.ppp_obytes;
                   (void) putc(PPP_FLAG, &tp->t_outq);
               }
   
               /* Calculate the FCS for the first mbuf's worth. */
               sc->sc_outfcs = pppfcs(PPP_INITFCS, mtod(m, u_char *), m->m_len);
               getmicrotime(&sc->sc_if.if_lastchange);
           }
   
           for (;;) {
               start = mtod(m, u_char *);
               len = m->m_len;
               stop = start + len;
               while (len > 0) {
                   /*
                    * Find out how many bytes in the string we can
                    * handle without doing something special.
                    */
                   for (cp = start; cp < stop; cp++)
                       if (ESCAPE_P(*cp))
                           break;
                   n = cp - start;
                   if (n) {
                       /* NetBSD (0.9 or later), 4.3-Reno or similar. */
                       ndone = n - b_to_q(start, n, &tp->t_outq);
                       len -= ndone;
                       start += ndone;
                       sc->sc_stats.ppp_obytes += ndone;
   
                       if (ndone < n)
                           break;  /* packet doesn't fit */
                   }
                   /*
                    * If there are characters left in the mbuf,
                    * the first one must be special.
                    * Put it out in a different form.
                    */
                   if (len) {
                       s = spltty();
                       if (putc(PPP_ESCAPE, &tp->t_outq)) {
                           splx(s);
                           break;
                       }
                       if (putc(*start ^ PPP_TRANS, &tp->t_outq)) {
                           (void) unputc(&tp->t_outq);
                           splx(s);
                           break;
                       }
                       splx(s);
                       sc->sc_stats.ppp_obytes += 2;
                       start++;
                       len--;
                   }
               }
   
               /*
                * If we didn't empty this mbuf, remember where we're up to.
                * If we emptied the last mbuf, try to add the FCS and closing
                * flag, and if we can't, leave sc_outm pointing to m, but with
                * m->m_len == 0, to remind us to output the FCS and flag later.
                */
               done = len == 0;
               if (done && m->m_next == NULL) {
                   u_char *p, *q;
                   int c;
                   u_char endseq[8];
   
                   /*
                    * We may have to escape the bytes in the FCS.
                    */
                   p = endseq;
                   c = ~sc->sc_outfcs & 0xFF;
                   if (ESCAPE_P(c)) {
                       *p++ = PPP_ESCAPE;
                       *p++ = c ^ PPP_TRANS;
                   } else
                       *p++ = c;
                   c = (~sc->sc_outfcs >> 8) & 0xFF;
                   if (ESCAPE_P(c)) {
                       *p++ = PPP_ESCAPE;
                       *p++ = c ^ PPP_TRANS;
                   } else
                       *p++ = c;
                   *p++ = PPP_FLAG;
   
                   /*
                    * Try to output the FCS and flag.  If the bytes
                    * don't all fit, back out.
                    */
                   s = spltty();
                   for (q = endseq; q < p; ++q)
                       if (putc(*q, &tp->t_outq)) {
                           done = 0;
                           for (; q > endseq; --q)
                               unputc(&tp->t_outq);
                           break;
                       }
                   splx(s);
                   if (done)
                       sc->sc_stats.ppp_obytes += q - endseq;
               }
   
               if (!done) {
                   /* remember where we got to */
                   m->m_data = start;
                   m->m_len = len;
                   break;
               }
   
               /* Finished with this mbuf; free it and move on. */
               m = m_free(m);
               if (m == NULL) {
                   /* Finished a packet */
                   break;
               }
               sc->sc_outfcs = pppfcs(sc->sc_outfcs, mtod(m, u_char *), m->m_len);
           }
   
           /*
            * If m == NULL, we have finished a packet.
            * If m != NULL, we've either done as much work this time
            * as we need to, or else we've filled up the output queue.
            */
           sc->sc_outm = m;
           if (m)
               break;
       }
   
       /* Call pppstart to start output again if necessary. */
       s = spltty();
       pppstart(tp);
   
       /*
        * This timeout is needed for operation on a pseudo-tty,
        * because the pty code doesn't call pppstart after it has
        * drained the t_outq.
        */
       if (!idle && (sc->sc_flags & SC_TIMEOUT) == 0) {
           sc->sc_ch = timeout(ppp_timeout, (void *) sc, 1);
           sc->sc_flags |= SC_TIMEOUT;
       }
   
       splx(s);
   }
   
   /*
    * This gets called when a received packet is placed on
    * the inq, at splsoftnet. The pppd daemon is to be woken up to do a read().
    */
   static void
   pppasyncctlp(sc)
       struct ppp_softc *sc;
   {
       struct tty *tp;
       int s;
   
       /* Put a placeholder byte in canq for ttselect()/ttnread(). */
       s = spltty();
       tp = (struct tty *) sc->sc_devp;
       putc(0, &tp->t_canq);
       ttwakeup(tp);
       splx(s);
   }
   
   /*
    * Start output on async tty interface.  If the transmit queue
    * has drained sufficiently, arrange for pppasyncstart to be
    * called later at splsoftnet.
    * Called at spltty or higher.
    */
   static int
   pppstart(tp)
       register struct tty *tp;
   {
       register struct ppp_softc *sc = (struct ppp_softc *) tp->t_sc;
   
       /*
        * Call output process whether or not there is any output.
        * We are being called in lieu of ttstart and must do what it would.
        */
       if (tp->t_oproc != NULL)
           (*tp->t_oproc)(tp);
   
       /*
        * If the transmit queue has drained and the tty has not hung up
        * or been disconnected from the ppp unit, then tell if_ppp.c that
        * we need more output.
        */
       if (CCOUNT(&tp->t_outq) < PPP_LOWAT
           && !((tp->t_state & TS_CONNECTED) == 0)
           && sc != NULL && tp == (struct tty *) sc->sc_devp) {
           ppp_restart(sc);
       }
   
       return 0;
   }
   
   /*
    * Timeout routine - try to start some more output.
    */
   static void
   ppp_timeout(x)
       void *x;
   {
       struct ppp_softc *sc = (struct ppp_softc *) x;
       struct tty *tp = (struct tty *) sc->sc_devp;
       int s;
   
       s = spltty();
       sc->sc_flags &= ~SC_TIMEOUT;
       pppstart(tp);
       splx(s);
   }
   
   /*
    * Allocate enough mbuf to handle current MRU.
    */
   static void
   pppgetm(sc)
       register struct ppp_softc *sc;
   {
       struct mbuf *m, **mp;
       int len;
   
       mp = &sc->sc_m;
       for (len = sc->sc_mru + PPP_HDRLEN + PPP_FCSLEN; len > 0; ){
           if ((m = *mp) == NULL) {
               MGETHDR(m, M_DONTWAIT, MT_DATA);
               if (m == NULL)
                   break;
               *mp = m;
               MCLGET(m, M_DONTWAIT);
           }
           len -= M_DATASIZE(m);
           mp = &m->m_next;
       }
   }
   
   /*
    * tty interface receiver interrupt.
    */
   static unsigned paritytab[8] = {
       0x96696996, 0x69969669, 0x69969669, 0x96696996,
       0x69969669, 0x96696996, 0x96696996, 0x69969669
   };
   
   /*
    * Called when character is available from device driver.
    * Only guaranteed to be at splsofttty() or spltty()
    * This is safe to be called while the upper half's netisr is preempted.
    */
   static int
   pppinput(c, tp)
       int c;
       register struct tty *tp;
   {
       register struct ppp_softc *sc;
       struct mbuf *m;
       int ilen, s;
   
       sc = (struct ppp_softc *) tp->t_sc;
       if (sc == NULL || tp != (struct tty *) sc->sc_devp)
           return 0;
   
       ++tk_nin;
       ++sc->sc_stats.ppp_ibytes;
   
       if ((tp->t_state & TS_CONNECTED) == 0) {
           if (sc->sc_flags & SC_DEBUG)
               if_printf(&sc->sc_if, "no carrier\n");
           goto flush;
       }
   
       if (c & TTY_ERRORMASK) {
           /* framing error or overrun on this char - abort packet */
           if (sc->sc_flags & SC_DEBUG)
               if_printf(&sc->sc_if, "line error %x\n", c & TTY_ERRORMASK);
           goto flush;
       }
   
       c &= TTY_CHARMASK;
   
       /*
        * Handle software flow control of output.
        */
       if (tp->t_iflag & IXON) {
           if (c == tp->t_cc[VSTOP] && tp->t_cc[VSTOP] != _POSIX_VDISABLE) {
               if ((tp->t_state & TS_TTSTOP) == 0) {
                   tp->t_state |= TS_TTSTOP;
                   tp->t_stop(tp, 0);
               }
               return 0;
           }
           if (c == tp->t_cc[VSTART] && tp->t_cc[VSTART] != _POSIX_VDISABLE) {
               tp->t_state &= ~TS_TTSTOP;
               if (tp->t_oproc != NULL)
                   (*tp->t_oproc)(tp);
               return 0;
           }
       }
   
       s = spltty();
       if (c & 0x80)
           sc->sc_flags |= SC_RCV_B7_1;
       else
           sc->sc_flags |= SC_RCV_B7_0;
       if (paritytab[c >> 5] & (1 << (c & 0x1F)))
           sc->sc_flags |= SC_RCV_ODDP;
       else
           sc->sc_flags |= SC_RCV_EVNP;
       splx(s);
   
       if (sc->sc_flags & SC_LOG_RAWIN)
           ppplogchar(sc, c);
   
       if (c == PPP_FLAG) {
           ilen = sc->sc_ilen;
           sc->sc_ilen = 0;
   
           if (sc->sc_rawin_count > 0) 
               ppplogchar(sc, -1);
   
           /*
            * If SC_ESCAPED is set, then we've seen the packet
            * abort sequence "}~".
            */
           if (sc->sc_flags & (SC_FLUSH | SC_ESCAPED)
               || (ilen > 0 && sc->sc_fcs != PPP_GOODFCS)) {
               s = spltty();
               sc->sc_flags |= SC_PKTLOST; /* note the dropped packet */
               if ((sc->sc_flags & (SC_FLUSH | SC_ESCAPED)) == 0){
                   if (sc->sc_flags & SC_DEBUG)
                       if_printf(&sc->sc_if, "bad fcs %x, pkt len %d\n",
                              sc->sc_fcs, ilen);
                   sc->sc_if.if_ierrors++;
                   sc->sc_stats.ppp_ierrors++;
               } else
                   sc->sc_flags &= ~(SC_FLUSH | SC_ESCAPED);
               splx(s);
               return 0;
           }
   
           if (ilen < PPP_HDRLEN + PPP_FCSLEN) {
               if (ilen) {
                   if (sc->sc_flags & SC_DEBUG)
                       if_printf(&sc->sc_if, "too short (%d)\n", ilen);
                   s = spltty();
                   sc->sc_if.if_ierrors++;
                   sc->sc_stats.ppp_ierrors++;
                   sc->sc_flags |= SC_PKTLOST;
                   splx(s);
               }
               return 0;
           }
   
           /*
            * Remove FCS trailer.  Somewhat painful...
            */
           ilen -= 2;
           if (--sc->sc_mc->m_len == 0) {
               for (m = sc->sc_m; m->m_next != sc->sc_mc; m = m->m_next)
                   ;
               sc->sc_mc = m;
           }
           sc->sc_mc->m_len--;
   
           /* excise this mbuf chain */
           m = sc->sc_m;
           sc->sc_m = sc->sc_mc->m_next;
           sc->sc_mc->m_next = NULL;
   
           ppppktin(sc, m, sc->sc_flags & SC_PKTLOST);
           if (sc->sc_flags & SC_PKTLOST) {
               s = spltty();
               sc->sc_flags &= ~SC_PKTLOST;
               splx(s);
           }
   
           pppgetm(sc);
           return 0;
       }
   
       if (sc->sc_flags & SC_FLUSH) {
           if (sc->sc_flags & SC_LOG_FLUSH)
               ppplogchar(sc, c);
           return 0;
       }
   
       if (c < 0x20 && (sc->sc_rasyncmap & (1 << c)))
           return 0;
   
       s = spltty();
       if (sc->sc_flags & SC_ESCAPED) {
           sc->sc_flags &= ~SC_ESCAPED;
           c ^= PPP_TRANS;
       } else if (c == PPP_ESCAPE) {
           sc->sc_flags |= SC_ESCAPED;
           splx(s);
           return 0;
       }
       splx(s);
   
       /*
        * Initialize buffer on first octet received.
        * First octet could be address or protocol (when compressing
        * address/control).
        * Second octet is control.
        * Third octet is first or second (when compressing protocol)
        * octet of protocol.
        * Fourth octet is second octet of protocol.
        */
       if (sc->sc_ilen == 0) {
           /* reset the first input mbuf */
           if (sc->sc_m == NULL) {
               pppgetm(sc);
               if (sc->sc_m == NULL) {
                   if (sc->sc_flags & SC_DEBUG)
                       if_printf(&sc->sc_if, "no input mbufs!\n");
                   goto flush;
               }
           }
           m = sc->sc_m;
           m->m_len = 0;
          m->m_data = M_DATASTART(sc->sc_m);
          sc->sc_mc = m;
          sc->sc_mp = mtod(m, char *);
          sc->sc_fcs = PPP_INITFCS;
          if (c != PPP_ALLSTATIONS) {
              if (sc->sc_flags & SC_REJ_COMP_AC) {
                  if (sc->sc_flags & SC_DEBUG)
                      if_printf(&sc->sc_if,
                                "garbage received: 0x%x (need 0xFF)\n", c);
                  goto flush;
              }
              *sc->sc_mp++ = PPP_ALLSTATIONS;
              *sc->sc_mp++ = PPP_UI;
              sc->sc_ilen += 2;
              m->m_len += 2;
          }
      }
      if (sc->sc_ilen == 1 && c != PPP_UI) {
          if (sc->sc_flags & SC_DEBUG)
              if_printf(&sc->sc_if, "missing UI (0x3), got 0x%x\n", c);
          goto flush;
      }
      if (sc->sc_ilen == 2 && (c & 1) == 1) {
          /* a compressed protocol */
          *sc->sc_mp++ = 0;
          sc->sc_ilen++;
          sc->sc_mc->m_len++;
      }
      if (sc->sc_ilen == 3 && (c & 1) == 0) {
          if (sc->sc_flags & SC_DEBUG)
              if_printf(&sc->sc_if, "bad protocol %x\n",
                        (sc->sc_mp[-1] << 8) + c);
          goto flush;
      }
  
      /* packet beyond configured mru? */
      if (++sc->sc_ilen > sc->sc_mru + PPP_HDRLEN + PPP_FCSLEN) {
          if (sc->sc_flags & SC_DEBUG)
              if_printf(&sc->sc_if, "packet too big\n");
          goto flush;
      }
  
      /* is this mbuf full? */
      m = sc->sc_mc;
      if (M_TRAILINGSPACE(m) <= 0) {
          if (m->m_next == NULL) {
              pppgetm(sc);
              if (m->m_next == NULL) {
                  if (sc->sc_flags & SC_DEBUG)
                      if_printf(&sc->sc_if, "too few input mbufs!\n");
                  goto flush;
              }
          }
          sc->sc_mc = m = m->m_next;
          m->m_len = 0;
          m->m_data = M_DATASTART(m);
          sc->sc_mp = mtod(m, char *);
      }
  
      ++m->m_len;
      *sc->sc_mp++ = c;
      sc->sc_fcs = PPP_FCS(sc->sc_fcs, c);
      return 0;
  
   flush:
      if (!(sc->sc_flags & SC_FLUSH)) {
          s = spltty();
          sc->sc_if.if_ierrors++;
          sc->sc_stats.ppp_ierrors++;
          sc->sc_flags |= SC_FLUSH;
          splx(s);
          if (sc->sc_flags & SC_LOG_FLUSH)
              ppplogchar(sc, c);
      }
      return 0;
  }
  
  #define MAX_DUMP_BYTES  128
  
  static void
  ppplogchar(sc, c)
      struct ppp_softc *sc;
      int c;
  {
      if (c >= 0)
          sc->sc_rawin[sc->sc_rawin_count++] = c;
      if (sc->sc_rawin_count >= sizeof(sc->sc_rawin)
          || (c < 0 && sc->sc_rawin_count > 0)) {
          printf("%s input: %*D", sc->sc_if.if_xname,
                  sc->sc_rawin_count, sc->sc_rawin, " ");
          sc->sc_rawin_count = 0;
      }
  }

Cache object: c6eea1c31b6ed21aad73d54d43522e92